Image description

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

The description adds a significant behavioral fact beyond the annotations: 'Costs credits from the account wallet.' This warns the agent that the call has a financial side effect, which is not captured by readOnlyHint, idempotentHint, or destructiveHint. No statement contradicts the annotations.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Three short sentences, front-loaded with the essential image-to-output behavior, followed by the use case and cost warning. Every sentence earns its place and there is no filler.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Without an output schema and with 0% parameter coverage, the description should clarify how to provide the image and what each purpose value produces. It does not explain the relationship between the image object and imageUrl, nor how the four purpose enum values change the result, leaving an agent to guess at invocation details.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 0%, so the description must compensate, but it never mentions the purpose parameter, its enum values, or the imageUrl alternative. The output list ('alt text, a caption, tags, and any text found inside') loosely hints at what purpose may control, but an agent cannot determine how to choose alt vs product vs detailed or when to use imageUrl instead of image.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description states the exact resource (an image) and the expected outputs (alt text, caption, tags, and any text inside the image). This makes it distinguishable from the many sibling parserail tools, none of which promise this specific image-description behavior.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

The phrase 'Accessibility and catalogs in one call' gives clear use-case context: generate alt text for accessibility or build image catalogs. It does not explicitly name alternatives or exclusions, but the intended context is clear enough for an agent to know when this tool applies.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.